In a cellular radio packet transmitting system using an orthogonal frequency division multiple access (OFDMA) scheme or a single carrier-frequency division multiple access (SC-FDMA) scheme used in uplink, uplink packets are distinguished by utilizing different time-frequency resources. In particular, in the transmission of the uplink packets of the cellular system, a base station transmits scheduling commands to mobile stations such that collision in uplink packet transmissions of different mobile stations is avoided and packet transmission suitable for a buffer state and a channel state of each mobile station is realized.
However, if an uplink packet scheduling command is transmitted in downlink whenever the uplink packet is transmitted, downlink overhead is extremely increased. Accordingly, in order to reduce downlink overhead in uplink packet transmission scheduling, a synchronous hybrid automatic repeat request (HARQ) scheme and a persistent scheduling scheme may be considered.
In the synchronous HARQ scheme, a mobile station performs a packet transmission according to a scheduling command received from a base station and performs a packet retransmission with respect to a packet for which negative acknowledgement (NACK) is received from the base station, using a previously used frequency band after a predetermined time elapses from a previous transmission timing or using a frequency band moved by the amount induced from a predetermined frequency hopping pattern if frequency hopping is further applied. Alternatively, a mobile station which receives a plurality of time-frequency resources available for a packet transmission in the future from a base station in advance, that is, a mobile station which receives persistent scheduling may perform a packet transmission using a predetermined time-frequency resource although a scheduling command is not received.
Several subpackets used for an initial transmission and a retransmission using the HARQ scheme are created from one codeword packet. The created several subpackets can be distinguished by the lengths of the subpackets and the start locations of the subpackets. A distinguishable subpacket is called a redundancy version (RV) and RV information refers to a promised start location of each RV.
A transmitter (Tx) transmits subpackets via a data channel in each HARQ transmission. At this time, the transmitter creates the RV of the subpacket for each HARQ transmission in sequence previously decided between the transmitter and a receiver or creates any RV and transmits RV information via a control channel. The receiver (Rx) maps the subpacket received via the data channel to an accurate location of a codeword packet in a predetermined RV sequence or using the RV information received via the control channel.
FIG. 1 is a view showing a HARQ transmission in case of using four fixed RV start locations. In addition, in FIG. 1, it is assumed that a static channel is used and the size of the subpacket used in each HARQ transmission is constant and is N/3. In FIG. 1, a first transmission indicates a subpacket used for an initial transmission using the HARQ scheme and the remaining transmissions indicate subpackets used for three HARQ retransmissions. In FIG. 1, N indicates the size of a circular buffer.
The base station may control a transmission of the mobile station, which receives dynamic scheduling, via an uplink scheduling command with respect to a new data packet of each mobile station, but may not transmit a scheduling command with respect to a retransmission packet. At this time, the mobile station performs a packet retransmission with respect to data, which is requested to be retransmitted from the base station, at a subframe separated from a previous packet transmission timing of the same data by a predetermined subframe interval. However, the mobile station detects whether the scheduling command is transmitted to the mobile station in downlink with respect to all the uplink subframes and performs a packet retransmission according to the command if the uplink scheduling command for the data to be retransmitted is detected.
In the persistent scheduling scheme, the base station allocates the time-frequency resource to the mobile station in a specific period in advance such that the time-frequency resource is used for the uplink packet transmission. The mobile station to which the persistent scheduling is applied may transmit an uplink packet with respect to the scheduled time-frequency resource although the scheduling command is not received.
In addition, the mobile stations in which the uplink packet transmissions are previously configured by upper-layer signaling like the persistent scheduling scheme may transmit packets using the predetermined time-frequency resources without the downlink scheduling command. When the retransmission is necessary with respect to the packets transmitted using the predetermined time-frequency resources, the synchronous HARQ operation may be applied.
A part of the uplink time-frequency resource in the cellular radio packet transmitting system may be reserved for a special purpose. As a representative example thereof, a time-frequency resource which is reserved such that the mobile stations which attempt to perform initial connection to a cell transmit a signal which is first transmitted in the cell, that is, a random access channel (RACH), may be used.
The mobile stations which attempt to perform the connection to the cell may transmit a physical RACH (PRACH) using a unit time-frequency domain occupying one or two subframes in about a 1.08-MHz band reserved for a PRACH transmission. The unit time-frequency domain for the PRACH transmission may be allocated according to one of 16 PRACH configurations shown in Table 1.
TABLE 1PRACHSystem frameConfigurationnumberSubframe number0Even11Even42Even73Any14Any45Any76Any1, 67Any2, 78Any3, 89Any1, 4, 710Any2, 5, 811Any3, 6, 912Any0, 2, 4, 6, 813Any1, 3, 5, 7, 914Any0, 1, 2, 3, 4, 5, 6, 7, 8, 915Even9
In Table 1, one system frame consists of 10 subframes, and 10 subframes in the system frame are denoted by subframe numbers of 0 to 9. At this time, the frequency location for a PRACH transmission in each subframe may move according to a predetermined frequency hopping pattern.
If specific time-frequency resources are reserved for special purpose, the transmission area for retransmission packets to be transmitted by the synchronous HARQ scheme and the packets to be transmitted by the persistent scheduling scheme may collide with the time-frequency resource reserved for the special purpose.
FIG. 2 is a view showing an example in which time-frequency resources for retransmitting the packets by the synchronous HARQ scheme collide with time-frequency resources reserved for a RACH transmission.
In the example of FIG. 2, the packets are retransmitted by the synchronous HARQ scheme in the unit of four subframes. Boxes 290 occupying four resource blocks on a frequency axis indicate the time-frequency resources reserved for the RACH transmission. At this time, resources 210 and 220 allocated to an initial transmission packet and a retransmission packet are shown at the upper side of FIG. 2 and resources 230, 240 and 250 allocated to an initial transmission packet, a first retransmission packet and a second retransmission packet are shown at the lower side of FIG. 2. A RACH time-frequency resource 290 collides with a first retransmission packet 220 and a second retransmission packet 250 shown at the upper side.